In recent years, the aviation industry has continued numerous efforts to reduce cost and improve performance of navigation avionics and flight control systems while maintaining or improving the level of safety. For example, an inertial reference system (IRS) for an aircraft includes gyroscopes and accelerometers to provide data concerning the state of the aircraft. Some of these data measurements (including pitch, roll, attitude, and heading) are transferred to one or more avionics displays in the aircraft. In addition, IRS signal data are also used to augment the aircraft's flight control system and to navigate the airplane.
Typically, a large commercial aircraft includes primary and secondary (for example, primary and standby) attitude and heading displays. Pilots will use the standby display in situations where one (or more) of the primary displays fails. In one implementation, two or more IRS systems generate attitude and heading signals for the primary displays, while the standby display has self-contained gyroscopes and accelerometers to generate its own attitude and heading signals. It is important that the attitude and heading signals for the standby display use a dissimilar design from the IRS of the primary displays to avoid any possibilities that a common design failure could adversely affect both the primary and the standby displays.
In addition, each aircraft generally has a “minimum equipment list” (MEL) that defines the minimum complement of equipment, such as inertial equipment, that is required for takeoff. For example, the inertial minimum equipment list for large-scale commercial aircraft might include (1) at least one source of IRS signals for navigation (in an event of the loss of navigation signals via a global positioning system, or GPS); (2) at least three independent sources of flight control inertial signals for the flight control system; (3) at least three independent sources of attitude signals for the primary displays; and (4) at least one source of attitude signals for the standby display.
Commercial airlines want to avoid flight delays and flight cancellations (for example, those delays caused by a failure within the inertial system). It is therefore desirable to provide adequate redundancy within the inertial system to allow dispatch (that is, allow the airplane to takeoff) even after a failure has occurred in the inertial system. This allows the airline to continue flying the aircraft on its original schedule, and to defer the repair to a convenient time and location. However, this inertial system redundancy directly affects the cost of aircraft avionics. Thus, there is a need for improvements in redundancy for aircraft inertial signal data.